As a per diem structural welder, your job is to work part-time or full-time to weld metal during the construction of various structures. As part of this, you may read the plans for each section you are asked to build, examine the materials, weld from aerial lifts, and maintain various tools. A per diem job either offers a day rate of pay or offers a daily allowance for living expenses on top of a salary or hourly pay. A per diem structural welder usually travels to work on a project, sometimes as a fill-in for other on structures for an extended period.